The present invention relates to a sublimation transfer method for producing dyed images, such as letters, symbols and patterns, on cloth goods such as shirts, and a heat-melt transfer medium used in the method.
Heretofore there is known a sublimation transfer method which comprises using a heat-melt transfer medium having on a foundation a heat-meltable ink layer containing a sublimation dye as a coloring agent, selectively melt-transferring the heat-meltable ink layer onto a sheet having a good absorptive property by heating with a heating head to prepare a master having an image of the ink, superimposing the master onto a substrate so that the image faces the substrate and heating the resultant master/substrate at a temperature not less than the heat-transfer temperature of the sublimation dye to transfer the dye to the substrate, thereby yielding a monochromatic dye image, and a heat-melt transfer medium used in the method (Japanese Examined Patent Publication No. 58080/1989). According to the sublimation transfer method, the master is prepared by using a thermal transfer printer. Therefore, the sublimation transfer method has the advantage that dye images of arbitrary letters, symbols or patterns (hereinafter those are generically represented by "patterns") can be readily formed on the substrate, as compared with a conventional sublimation printing method.
However, the above-mentioned sublimation transfer method and the transfer medium used therein have the following drawbacks.
When the content of sublimation dye in the heat-meltable ink layer is increased in order to increase the density of the dye image in the above method, the ink layer has a poor adhesiveness to a sheet for a master, which results in failure to form a master with a clear image. Further, the portion of the heat-meltable ink layer that is heated with a heating head does not necessarily have a sufficient releasability from the foundation, which also results in failure to form a master with a clear image.
In particular, when the sublimation transfer method and the transfer medium are applied to the formation of polychromatic or full-color dye images, the poor releasability and adhesiveness of the heat-meltable ink layer cause serious problems.
In the formation of full-color dye images, two or more kinds of ink dots selected from a heat-meltable ink layer containing a yellow sublimation dye, a heat-meltable ink layer containing a magenta sublimation dye and a heat-meltable ink layer containing a cyan sublimation dye must be superimposed one on another on the sheet for a master. When the conventional method is applied, the superimposition of such ink dots is not favorably effected because of the poor releasability of the ink dots from the foundation and the poor adhesiveness of ink dots one on another, which results in failure to form a desired full-color dye image.
In the case of forming a full-color dye image, plural gradations are required for each color. However, if the release of ink dots and the superimposition of ink dots one on another are not favorably effected, a desired gradation cannot be obtained.
In the case of producing a plurality of gradations by an area-modulation method with respect to a color, for example, a picture element is composed of 2.times.2 dot matrix and the number of dots included in the dot matrix is varied within the range of 1 to 4, thereby giving four gradations for the color. In this case, if ink dots are favorably released from the transfer medium or an ink dot is not favorably adhered to the master sheet or another ink dot which has been transferred to the master sheet, a predetermined number of ink dots cannot be deposited to the predetermined positions within the matrix, which results in failure to obtain a desired gradation.
It is an object of the present invention to provide a sublimation transfer method wherein ink dots are readily released from the transfer medium and the ink dots are well adhered to a sheet for a master to give a master with a clear image, which results in the formation of a clear dye image on a substrate; and a heat-melt transfer medium used in the method.
Another object of the present invention is to provide a sublimation transfer method which gives a master having an excellent full-color ink image, resulting in the formation of an excellent full-color dye image on a substrate.
These and other objects of the invention will become apparent from the description hereinafter.